666 



CIRCULATION. 



of the arteries as of a muscular nature, was un- 

 successful in producing obvious contractions in 

 them. The repetition of the experiments of 

 Verschuir by many others has been attended 

 with very various results ; some confirming his 

 observations, others having entirely failed in 

 producing any obvious contraction, or not being 

 disposed to consider it of a muscular kind. 

 Among the last may be mentioned Nysten, 

 Bichat, Wedemeyer, and J. Miiller. 



It must be obvious that, laying aside the 

 difference of opinion regarding the nature of 

 the contractions when they are admitted to 

 occur, in a question of this kind a positive re- 

 sult deserves more consideration than a nega- 

 tive one, provided the phenomena stated to 

 have been observed are such as to be appre- 

 ciable by all. Among the experiments favour- 

 able to the view that the large arteries are en- 

 dowed with irritability, may be mentioned those 

 described by Hastings,* and a series of unpub- 

 lished observations by Dr. Thomson, to which 

 we have access, which seem to prove in a very 

 satisfactory manner the frequent occurrence of 

 contractions in the larger arteries after stimula- 

 tion ; and to point out as a cause of the failure 

 of some at least of the previous experiments, 

 the long time which commonly elapses between 

 the application of the stimulus and the occur- 

 rence of the contraction ; together with the cir- 

 cumstances formerly remarked by Verschuir, 

 that the contraction is not an invariable conse- 

 quence of the stimulation, and that it occurs 

 much more readily in some animals than in 

 others. 



According to Dr. Thomson the contraction 

 of the larger arteries is in general not percepti- 

 ble before from three to ten minutes after the 

 application of the stimulus. When galvanism 

 is "used, the shocks need not be strong, but 

 must be frequently repeated in order to induce 

 contraction. 



Many have remarked the gradual or sudden 

 contraction of the trunks of arteries which have 

 been laid bare in Man as well as in the lower 

 animals. When exposed, an artery is some- 

 times equally contracted for some length along 

 its tube ; at other times its surface assumes a 

 waved appearance from the occurrence of irre- 

 gular contractions or alternate contractions and 

 dilatations, and not unfrequently the coat of 

 the artery is much constricted at one point 

 only, as if a tight cord had been passed round 

 it. Appearances of this kind, which seem to 

 indicate very distinctly the possession of the 

 property of irritability by the arteries, are well 

 known to many surgeons ; they were noted by 

 Drs. Jones and Thomson, in "the experiments 

 upon which Dr. Jones's work on Hemorrhage 

 was founded ; and also by Dr. Parry, who 

 nevertheless refuses to consider them as irri- 

 table contractions. At p. 74 of his work 

 on the Powers of the Arteries, Dr. Parry, 

 referring to Experiment 13th, says, " thus a 

 very narrow ring of the carotid became, while 

 it was under examination, contracted as if a 



* Inaug. Dissertat. Edin. 1817, et loc. cit. See 

 also Hunter on the Muscularity of the Arteries, 

 Edin. Med. and Surg, Journ. xxii. p. 256. 



small ligature had been half tightened around 

 it.' 7 So also in Experiment 24th, he relates 

 that a part of the carotid artery of a ewe was 

 diminished by a third of its original diameter 

 underexposure, after having been half an hour 

 denuded, while the neighbouring parts had be- 

 come rather dilated, and that while he was pro- 

 ceeding to measure one of these dilated por- 

 tions, he " saw it shrink to nearly the same 

 size as the constricted part." It appears to us 

 manifest, that, whether these irregular diminu- 

 tions of the diameter of the artery, obviously 

 occasioned by a shortening of its fibres, are at- 

 tributed to the exposure of the artery to the air, 

 or the violence done during the dissection of it 

 by the scalpel, they must equally be regarded 

 as the consequence of stimulation of one kind 

 or other, and are therefore of the nature of mus- 

 cular contractions. 



Hoffmann first noticed the contractions of 

 the arteries from the application of acrid che- 

 mical stimuli to their coats; and it appears 

 from numerous subsequent experiments, that 

 contractions are more readily induced in this 

 than in any other way. Were there no other 

 proofs of the contractility of the arteries than 

 those derived from the effect of chemical 

 agents, we should not feel inclined to place 

 much reliance on them, on account of the pos- 

 sibility of there having been induced a perma- 

 nent alteration of the texture from chemical 

 action ; but the results of such experiments 

 form an important confirmation of those which 

 are performed with mechanical and galvanic 

 irritation. We cannot, however, acquiesce in 

 the opinion of Wedemeyer* and others who 

 compare the distinct and well-marked contrac- 

 tions of particular parts of the arterial tubes, 

 such as those above alluded to, to the general 

 constriction of other textures, and more parti- 

 cularly to the shrinking of the skin which 

 occurs from the influence of cold, passions of 

 the mind, &c. 



From these considerations we are induced to 

 adopt the opinion that the contractions which 

 under certain circumstances occur in the ar- 

 teries resemble muscular contractions more 

 nearly than any other vital phenomenon. The 

 positive evidence of direct experiment obviously 

 proves that the contractions in general follow 

 the application of some stimulus to the artery ; 

 but these contractions differ from that of mus- 

 cular parts chiefly in the length of time which 

 elapses after the application of the stimulus 

 before the change of size begins, in the slow- 

 ness with which the contraction is succeeded 

 by relaxation, and in the want of obvious cor- 

 respondence between the force of the stimulus 

 and the extent of contractions which follow it. 



Besides the more marked contractions of 

 parts of their tubes, the arteries are subject in 

 various circumstances to undergo a slow and 

 gradual diminution of their diameter through- 

 out their whole length, which is considered by 

 many physiologists to indicate the possession 

 by them of a property of the nature of contrac- 

 tility different from irritability in its pheno- 



* Loc. cit. 



